Process of producing urea.



UNITED STATE s PATENT OFFICE.

JOHN E. BUCHEB, OF COVENTRY, RHODE ISLAND, ASSIGNOR TO NITROGEN PRODUCTSCOMPANY, OF PROVIDENCE, RHODE ISLAND, A CORPORATION OF RHODE ISLAND.

rnoonss or i nonncme UREA.

No Drawing. Original apg October 21, 1915.

.To all whom it may 00% em:

Be it known that JOHN E. BUCHER, a citizen of the United States,residing at Co entry, in the county of Kent and State of Rhode Island,have invented certain new and useful Improvements in l rocesses ofProducing Urea, of which the following is a specification.

This invention relates to an improved process for the manufacture ofurealand, in its preferred form, the process is based upon theinteraction of metallic cyanates and ammonium compounds under conditionswhich particularly favor the formation and rec )vcry of urea.

Heretofore, urea has generally been made by heating solutions ofalkalicyanates with solutions of ammonium salts of oxygen containingmineral acids, such as the sulfate and nitrate. In many cases, theresulting solutions were then evaporated to dryness and the ureaextracted with solvents such as alcoholor methylated spirit.

In one form of my process, a strongsolution of preferably (but notnecessarily) highly soluble cyanate, such as that of potassium, may betreated with the requisite quantity of ammonia, and carbon dioxid isthen passed into this alkaline solution; suitpble temperature and.pressure conditions being of course observed during the several steps ofthe process.

A considerable part of the potassium precipitates out in the form ofpotassium bicarbonate wlth the formation of ammonium cyanate Theammonium cyanate, especially upon heating, changes to urea according tothe well known equationz' 2 nnponsoomng, The transformation of ammoniumcyanate (equation 2) into urea, which latter is onlyslightly-.dissociated, is fairly complete and becomes practicallyquantitative upon evaporating the water. This'changereduces theconcentration'of ammonium cyanate or the ions resulting from'itsdissociation and consequently it overcomes, in a large 'measure,the'factor which,'by opposing the formation Specification oi LettersPatent. I

solution becomes too Patented Oct. 2, 1917.

cation filed July 3, 1914, Serial No. 848,799. Divided and. thisapplication filed Serial No. 57,095.

of potassium bicarbonate, makes equation 1 incomplete.

If desired the concentration of urea may be made still higher by theaddition of solid alkali cyanate either before or after the removal ofthe original precipitate of potassium bicarbonate. The strengthening ofthe solution by the addition of solid alkali cyanates is especiallyadvantageous when sodium cyanate, which is much less soluble thanpotassium cyanate, is used.

On account of the great difference in solubilities, a strong solution ofurea with comparatively small quantities of the alkali compound isobtained. The urea can very easily be separated from the alkalicompounds in pure condition by taking advantage of the differing ratesof chan'ge'of solubility with the temperature Distillation of water maybe carried on I under diminished pressure, or, in a current of carbondioxid so as to prevent the change by neutralization due to theformation of ammonia urea.

When sodium cyanate is used, the change of this sparingly soluble acidsodium carbonateto the more soluble normal carbonate oifers anothermethod of separating pure ureaand it may even be changed intentionallyby the addition of free alkali such as ammonia. For example:

Pure urea can only crystallize from such a solution so long as thelatter remains unsaturated with bicarbonate. If now ammonia be added,the acid carbonate will be changed to the much more soluble normalcarbonate, and further large quantities .of pure urea may be obtained bycontinuing the crystallization of the urea until the normal by thehydrolysis of cyanate or carbonate begins to separate out. The solutionmay then again be saturated with carbon dioxid to remove, by furtherprecipitation, a considerable part of the remaining sodium asbicarbonate, and the just described process may be repeated until themonium carbonates. It is then returned to the initial part of theprocess for the preparation'of another portion of urea according toequation 1.'

much charged with ami may be obtained '111 my ap Many forms of apparatusmay be used but, since those forms at present employed commerciall inthe ammonia-soda process are peculiari; well adapted for this method ofreparing urea, no special apparatus nee be exemplified.

The sodium cyanate and the ammonia from any source, but both arepreferably obtained from atmospheric nitrogen. I prefer to fix thenitrogen according to the equation:

with'ja heated mixture of sodium carbonate, finely divided iron andcarbon as described lication for Uni-ted States Letters Patent, erialNumber 799,798, filed Nov. 7, 1913, and entitledMethod of fixinnitrogen, and then to distil out the cyani under diminished pressure asdescribed in The molten oyanid distillate is then treated with air at alow red heat according to the exothermic reaction:

- (4) NaGN+air=NaOCN+nitrogen This procedure, since it uses the moltencyanid as obtained from the distillation process, has the greatadvantage of not reuiring the heating up and the melting of t e cyanid,of 'ving out heat which can be utilized, and giv1nga practicallyunlimited" supply of substantially pure atmospheric nitrogen for'thecyanid eration nation 3), v

the product may then be used directly. as so um cyanate while the restis very readily converted into ammonia and sodium carbonate by theaction of hot water,

or steam, thus furnishing both the cyanate and ammonia, as well as apart of the carbon dioxid, which are required in equation 1:

The alkali compounds as well as the carbon dloxid thus actcyclicallyyand air, water and carbon comprise all the elements enteringinto urea. 's procedure becau'seof using organic acids tage of avoidingthe use of mineral acids, such as sulfuric, or neutralizing theammoniawhen such salts as ammonium sulfate are used for thepreparationof urea.

cyanate of urea into ammonia during the process causes no loss of ureaas it may be compensatedby using somewhat more than 5( 0 of the nitrogenrequired in equation 1 in the form of cyanate eyanate may produce somehf the requisite ammonia directly in the liquid in which the urea is tobe prepared. 7

I am aware that various-changes. may be made in my process and that thesteps of potassium bicarbonate.

forming ophas the further tam-- cipitate of said e above mentioneddecomposition of f so thatlthis excess of the method, as I havedescribed them by way of exemplification, may be varied or alternatedwidely, without departing from the spirit of my invention, and I, hence,desire to be limited only by the scope of the ap ended claims. 7

or example, instead of using ammonia and carbon dioxid; acid ammoniumcarbonate may be employed, and since both potassium cyanate and urea arehighly soluble, the former may be practically treated with .acidammonium carbonate to form In the case of alaline earth cyanates such asthose of barium or calcium, where the relative solubility of normalacidcarbonates is just the reverse of what it is in case of sodium, it ishighly desirable to elfect the formation of the practically insolublenormal carbonates as per the equation:

so as to precipitate the metal substantially quantitatively, in orderthat even the necessity for se aration by crystallization may beavoided. Idre it is only necessary to filter out the recipitatedcarbonate and then evaporate directly to dryness in order to get theurea.

It should be here observed, therefore, that in the claims the termalkali metal is to be regarded as of suificient breadth to include allof those metals of the alkali and alkaline earth metal groups which areavailable for use in the process. I

In general, 'I believe that the use of a suitable salt of an organicacid, in contradistinction to a mineral acid salt, is broadly new; andobviously, of course, the ammo- IllllIIl stlt of, for example, carbonicacid,

may be'supplied as such or it may be formed less evanescently during thecourse of theprocess, as by introducing carbon dioxid into the ureayieldin mass. Finally while it is pre erredto use carbonic acid, I donot desire to be limited to this latter since the broadly contemplatesthe re-action upon a metallic cyanate, in the presencepf monium salt ofany suitable acid which will form such a sparingly'soluble acid saltwith the metal of the cyanate as to 've a preacid salt'when t e latteris ormed together with ammonium cyanate.

he present case comprises claims which have been divided out'of theparent a plication hereof, Serial No. 848,799, filed uly 3, 1914, andentitled- Process of producing urea.

Having thus described my invention what I claim is:

1. The process of forming urea which comprises reacting upon a metalliccyanate, in the presence of water, with an ammonium salt of an acidwhich forms such a sparingly :water with an am-- soluble acid salt withthe metal of the cyanate as to give a precipitate of said acid salt whenthe latter is formed together with ammonium cyanate, generating saidammonium salt in the solution while effecting the reaction thereof uponsaid metallic cyanate, by treatment of the solution with ammonia and agaseous reagent'which combines with water to form the acid from whichsaid ammonium salt is derived, converting said ammonium cyanateintourea, and separating said precipitate from the urea.

2. The comprises reacting upon a metallic cyanate, in the presence ofwater, with an ammonium salt of an acidwhich forms such a sparinglysoluble acid salt With the metal of the cyanate as to 've a precip vtateof said acid salt when the atter is formed together with ammoniumcyanate, generating said ammonium salt in the solution while effectingthe reaction thereof upon said metallic cyanate, converting saidammonium cyanate into urea, and separating said precipitate from theurea. I

3. The process of forming urea which comprises reacting upon a metalliccyanate,

in the presence ofwater with an ammonium salt of an acid'jvhich formssuch a sparingly soluble" acid salt with the metal of the cyanate as togive a precipitateof said acid salt when the latter is formed togetherwith ammonium cyanate, generating said ammonium salt in the solutionwhile efiecting 'the reaction thereofupon said metallic cyby' treatmentof the solution with amanate, monia and an'anhydrous reagent whichcombines with Water to form the acid from which the ammonium salt isderived, con- Copies of thispatent may be obtained process of "formingurea which for five cents each, by addressing the Washington, D. 0.

the reaction thereof'upoii said metallic cyanate', by treatment of thesolution with ammonia and an anhydrous reagent which combines with waterto form the acid from which the ammonium salt is derived, convertingsaid ammonium cyanate. into urea, and separating said precipitate fromthe urea a portion at least of the required ammonia for sald solutionbeing generated by the decomposition of the said cyanogen compound insaid Water.

5. The process of forming urea which comprises reacting upon an .alkalicyanate with an ammonium salt of carbonic acid in the presence of water,to form ammonium cyanate and an acid alkali salt of carbonic acid,converting said ammonium cyanate. into urea, and separating thelatterfrom the residues of the reaction by distilling ofl tne waterwhilepassing carbon dioxid through the liquid to prevent the change ofalkali bicarbonate to-neutral carbonate.

In testimony whereof I have afiixed my signature, in the presence of twowitnesses. JOHN E. BUCHER. Witnesses:

HOWARD FQHY AND, HELEN M. BABNBROOKQ Commissioner of Patents,

forming urea which

